The influence of familiarity with clay and of language upon performance of traditional tasks involving conservation of quantity and weight was examined. 80 Tzeltal-speaking Indian children from two neighboring villages in the highlands of Chiapas, Mexico (aged 6-13) participated in the study. Conservation improved with age but the rate of improvement was slower than that predicted by US middle-class norms. Children from a village in which all women are potters did not perform differently from their peers in a neighboring village on any task. These results were discussed in terms of the influence of language and culture on children's assumptions about the strategies appropriate to the demands of the testing situation, and in terms of the specific nature of the potters' children's experience with clay. Subjects exhibited greater success with conservation of weight than quantity and a linguistic explanation for this finding was proposed. Inglés